BPL has been used over Low Voltage (LV) lines for in home networking applications and over Medium Voltage (MV) distribution lines for last mile access of broadband and smart grid applications. This is the first adaptation of this technology for station to station communications over electrical transmission lines. The characteristics of electrical transmission lines are a good match for BPL since the line loss (measured in, for example, dB per linear feet) is much lower than MV distribution lines, and there are few or no taps connected, to the line. The topology is a point to point straight line without branches, which translates to a longer distance of signal reach. The main technical challenge is maintaining BPL communications in a harsh electrical environment. The present invention provides a stable, high performance and highly available communication system over HV.
Traditionally, utilities used various communications technologies to connect their substations. Those are divided into two categories: in line and off line. Off line communication methods include: fiber optic cables, telephone copper wire, microwave RF radios, and wireless leased lines. The only in line communications methods so far have been Power Line Communications (PLC) over the existing power lines and fiber embedded in the ground wire called OPGW—Optical Ground Wire. Applications that use station-to-station communications are: protective relaying and line control, supervisory control and data acquisition (SCADA) management, sensing and power quality monitoring, voice services, and video surveillance.
Most recently with the advancements in digital technology, superior digital protection schemes such as line current differential, and superior sensing schemes such as synchrophasors, have become available. These and other new smart grid applications will require more bandwidth than the existing narrowband methods can provide. The use of broadband communications technologies such as fiber and HVBPL (High Voltage BPL) enables the deployment of such advanced methods of protection, monitoring and control. The term HVBPL is used herein to cover all transmission and sub-transmission voltages, even though the electric industry definition of HV is for 138 KV and above. Since the HVBPL technology uses the utility's own wires, there is a significant cost benefit (e.g. 10 to 1) compared to fiber, and it significantly reduces the deployment time, and simplifies the installation process.
A substation is typically used as a distribution point for transmission lines coming into the station and for multiple MV distribution feeders going out of a station to serve residential, commercial and industrial customers. The transmission lines terminate on the primary side of a step down transformer inside the substation, and the distribution lines are connected to its secondary side. The utility network uses a star topology over the distribution grid with the station being at its center. Substations usually cover an area of 3-5 square miles and are interconnected over transmission or sub-transmission lines. Typical voltage ratings used for sub-transmission lines in North America are 34 KV, 46 kV, and 69 kV (voltage rating in Europe and other parts of the world may be different).
Electric transmission lines are better balanced, more uniform and have lower losses than MV distribution lines. This is due to the fact they run in point to point mode between stations and do not branch like MV lines. They also have far fewer taps and discontinuities than MV lines do. This topology difference is a key factor in achieving better performance and longer distance of the BPL signal. Another difference is in the quality of the conductor wire and the quality of the construction. This difference is represented in a lower loss of energy and a longer distance of the transmitted signal measured in, for example, dB per feet.
Below is a list of U.S. patents that describe the method of using electrical power lines as a communications medium for delivery of broadband data. This technology is now known as Broadband over Powerline or BPL. Broadband is defined as transmission over 1 MHz (typically from 1 MHz to 50 MHz) and typically has data rates of multiple Mbps.
Broadband over Powerline (BPL) Patents5,684,450Electricity Distribution and/or Power TransmissionNetwork and Filter for Telecommunications overPower Lines5,929,750Transmission Network and Filter Therefore5,933,071Electricity Distribution and/or Power TransmissionNetwork and Filter for Telecommunication overPower Lines6,144,292Powerline Communications Network Employing TDMA,FDMA and/or CDMA6,172,597Electricity Distribution and/or Power TransmissionNetwork and Filter for Telecommunication overPower Lines6,282,405Hybrid Electricity and TelecommunicationsDistribution Network